Geo9 Modbus Register 1903: HeatPump Ambient T20

Technical Definition

The register HeatPump Ambient T20 at address 1903 is used to monitor heatpump ambient t20 on the Geo9.

• Protocol: Modbus RTU
• Data Type: S WORD
• Unit: °C
• Access: Read Only

How to Read (Python pymodbus)

Use this code snippet to read this specific value via RS485:

from pymodbus.client.sync import ModbusSerialClient

client = ModbusSerialClient(method='rtu', port='/dev/ttyUSB0', baudrate=9600)
client.connect()

# Read HeatPump Ambient T20 (Address: 1903)
# Note: Check if your device uses 0-based or 1-based addressing
result = client.read_input_registers(address=1903, count=2, unit=1)

if not result.isError():
    print(f"Raw Value: {result.registers}")
else:
    print("Error reading register")

client.close()

Integration (Home Assistant)

Paste this into your configuration.yaml:

- platform: modbus_controller
  name: "HeatPump Ambient T20"
  address: 1903
  value_type: S_WORD
  unit_of_measurement: "°C"

Connection Diagram

Here is the standard RS485 wiring for this configuration:

graph TD
    PLC[Host Controller / Home Assistant]
    Device[Geo9]

    PLC -- "A+ (D+)" --> Device
    PLC -- "B- (D-)" --> Device
    PLC -- GND --> Device

💡 Engineer's Insight

Analysis: Ambient Temperature (T20) measured by the heat pump. Units: °C. Typical range: -20-35°C.

Troubleshooting: Defective Temperature sensor, poor sensor placement, or HVAC system issues affecting local Temperature. Check for obstructions.